Field of the Invention
One disclosed aspect of the embodiments relates to an image processing apparatus and an image processing method.
Description of the Related Art
Image transformation processing may be required in an image processing apparatus. For example, to prevent a trapezoidal distortion from occurring in a projected image, a projector apparatus performs image transformation processing called keystone (trapezoidal) correction processing in which image transformation is performed so that an image projected on a screen becomes rectangular-shaped. To perform image transformation processing such as keystone (trapezoidal) correction processing, the projector apparatus stores an input image in a frame memory and then generates, through interpolation, pixel values of coordinates of an output image from neighborhood pixels in the coordinates of the input image each corresponding to a different one of coordinates of the output image. The bicubic interpolation method is an example of an interpolation method.
When image transformation processing is performed on an image, an image quality degradation called moire (interference fringes) may arise. Moire refers to interference fringes caused by the difference between the pixel pitch of the output image and the pitch of the coordinates, on the input image, each corresponding to a different one of the pixels of the output image. Image quality degradation due to moire is caused by high-frequency components of an original image. Japanese Patent Application Laid-Open No. 2010-26870 discusses a technique for performing smoothing processing to eliminate high-frequency components to reduce moire. In the technique discussed in Japanese Patent Application Laid-Open No. 2010-26870, moire in an image into which an original image has been transformed based on a predetermined rule is reduced. More specifically, in the technique, the transformation ratio of the transformed image with respect to the original image for each pixel is derived to perform smoothing processing with the intensity varied according to the transformation ratio.
However, to reduce moire through the above-described method in various cases of image transformation processing, it is necessary to perform transformation ratio derivation processing corresponding to each case of the image transformation processing. If the transformation ratio derivation processing is performed for each case of required image transformation processing, this method enables applying suitable moire reduction processing only to predetermined image transformation processing. With this method, suitable moire reduction processing cannot be applied to image transformation processing different from the predetermined image transformation processing.